Developing a friction performance index for asphalt concrete mixtures
For the majority of asphalt mixtures produced in the U.S., their design is
based solely on volumetric considerations. For a small but growing number of
these mixtures, the design may also be based on structural performance, e.g.,
balanced mixture design (BMD). With the BMD concept and/or changes to the current design
methodology, it is likely that mixtures will become finer, have an increased
asphalt content, and potentially higher amounts of recycled materials. All of
these changes will affect the functional characteristics; however, there does not currently exist a
methodology to assess asphalt mixture designs to ensure that their functional
performance characteristics. Worse, engineers lack a
reliable, vetted procedure to consider functional performance at the mixture
design stage. As such, state DOTs cannot actively engineer asphalt mixtures to
exhibit sufficient functional and structural performance thresholds. Thus, they
rely on ad hoc corrections when issues are identified.
This project will address this need by developing a
procedure for state DOTs to evaluate their mixtures to either screen for those
with poor functional performance or (ultimately) to design mixtures to avoid functional
failures associated with material characteristics that do not balance
functionality with structural durability. The experiences in developing
balanced mixture design practices for rutting and fatigue demonstrate that
failure to consider the consequences of potential test implementation (for
example implementing a rutting test without including a cracking test) drives
mixture behaviors in unexpected and unforeseen ways.
This research will address this problem by identifying
the most effective, discriminating, and implementable test method or methods
that state DOT’s can adopt and that other researchers can use to develop
practical mixture design methodologies and also for quality assurance
approaches. This project would be clearly aligned with the AASHTO Committee on Materials
and Pavements, which is concerned with, among other things, asphalt materials
testing, specification, and performance, as well as management. Given the
connection between the surface condition of roadways and safety, this research
also addresses the strategic goals for the Safety committee whose primary goal
is to eliminate serious traffic crashes and save lives.
The objectives of this research are to
develop a methodology, applicable to both the mixture design/selection
procedures and quality assurance/quality control process, to assess the
functional performance of asphalt concrete mixtures with respect to friction
and macrotexture. A draft set of tasks that will likely need to be performed to
achieve this goal are:
· Review existing
methodologies for determination of asphalt mixture texture and friction and
ongoing research in this domain.
The evaluation should consider the role of friction and texture in safety (as
defined by AASHTO and in NCHRP Report 37) and availability of datasets such as
continuous friction measurement data, asphalt mix design, and crash data.
· Select the most promising
experimental method(s) to evaluate asphalt mixture performance with respect to
friction and texture that can be applied during design and after construction.
· Develop the methodology for
performance assessment. This methodology should be capable of evaluating
asphalt mixtures macrotexture and microtexture but could consist of a
combination of component material and composite tests and models.
· Establish initial
performance thresholds for evaluation at the mixture design stage and for
process control and quality assurance, and refinement in later research.
Develop a draft AASHTO specification(s) for
review and submission as a provisional specification.
There is an urgent need for this work to address
the unknown impacts on safety (i.e. friction qualities) of asphalt mixtures as
the balanced mix design method is implemented by agencies. Developing a means
of evaluating functional performance properties that can be applied both during
design and post-production will allow functional performance and safety to be
designed into asphalt mixtures, and will provide a means of ensuring that this
performance is maintained through the QC/QA process
results of this research will be used by state DOTs (specifically state DOT
materials engineers), asphalt mixture designers, and asphalt paving contractors
to ensure that asphalt mixtures are designed and produced with balanced
structural and functional performance. Implementation activities may include:
presentations (e.g. TRB Annual Meeting, RPUG, AASHTO), regional user-producer
group presentations, BMD workshops, and webinars (e.g. TRB, AASHTO).
supplementary materials could include: a technical brief, short instructional
videos, and whiteboard videos.
national workshop or webinar with invited participants for discussion on
implementing the inclusion of functional assessment as part of mixture design
and quality assurance/quality control processes.
of a follow-up effort to formulate guidelines to help state DOTs implement the
functional assessment methodology into their mixture design and quality
with state DOTs currently participating in TPF-5(345/463) or similar studies.
|Sponsoring Committee:||AKP50, Pavement Surface Properties and Vehicle Interaction
|Research Period:||24 - 36 months|
|RNS Developer:||Shane Underwood and Boris Goenaga, North Carolina State University, 919-515-8632, email@example.com|
|Index Terms:||Friction factor, Index numbers, Asphalt concrete, Asphalt concrete pavements, Asphalt mixtures, Mix design, |
Safety and Human Factors